On Dec. 23, 1992, Kate Everding received an unusual Christmas present: her voice.

A few months before, the Silver Spring woman had undergone surgery to remove a tumor from her neck. The procedure paralyzed the nerve on the left side of her vocal cords, leaving her unable to speak above a harsh whisper.

But a tiny, two-part device implanted in her throat by Johns Hopkins surgeons changed that.

"You have to cooperate during the operation. You have to talk and sing," she said yesterday at a news conference in Baltimore. "And the effect is immediate: I walked out and talked."

The implant could help about 80 percent of patients whose vocal cords are partially paralyzed by surgery or accidents, or in some cases of impairment from Lou Gehrig's or Parkinson's diseases, said Dr. Charles W. Cummings, head of the Otolaryngology Department at the Johns Hopkins Medical Institutions.

It also offers relief to some people whose vocal cords have been severely weakened by age.

Hopkins has implanted the device in 39 people. Of those, one patient had a swollen neck when the implant shifted and one had complications from a separate injury.

The U.S. Food and Drug Administration has approved the implant for clinical testing at three additional sites, Dr. Cummings said.

During speech, vocal cords come together and then vibrate, stretching or clenching depending on pitch. When the nerve on one side of the vocal cords is damaged, the muscle on that side atrophies, preventing the vocal cords from closing, explained Dr. Paul W. Flint, director of otolaryngology at Hopkins Hospital.

An implant bolsters the immobile muscle. The healthy side then is able to close against the weak side of the vocal cords, enabling the patient to produce noise.

People with vocal cord nerve damage may make a breathy noise when they talk, as air leaks out around the disabled muscle, or they may sound hoarse or be limited to a whisper, Dr. Cummings said. They often choke on food.

The surgery used to implant the Hopkins device is not new. Developed in the 1970s by a Japanese doctor, it is being used elsewhere, including the University of Maryland Medical Center.

What is new about the Hopkins implant is that it is made of hydroxylapatite, a calcium and phosphate compound that resembles bone.

The advantage is that body tissue interacts with and grows onto it, which helps holds the implant in place, Dr. Cummings said. Previously, other implants have been made of a nonreactive plastic.

The Hopkins device also comes in five standardized sizes, an innovation that reduces the length of the implant operation. Otherwise, surgeons must tailor the size of each implant during surgery.

Doctors cut a "window" in the neck, giving them access to the vocal cords. They then try the implants on for size, using a long, thin implement. Throughout this procedure, the patient, who has received local anesthetics, is asked to talk and sing to help the doctors decide what size sounds best.

Once in place, the two pieces of the implant clamp together. If the implant doesn't fit or work well, it can be removed and replaced, Dr. Cummings said. For example, Ms. Everding was refitted three months after her original surgery.

The use of a bonelike material and standardized sizes are advances in thyroplasty, as vocal cord implant surgery is called, said Dr. Brian Flowers, assistant professor of laryngology at the University of Maryland School of Medicine, who uses the Japanese surgical technique.

"What's neat is the standardization, so you could be in the operating room and say 'I'll take a No. 5,' " he said.